1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to an apparatus and method for controlling a base station transmitted forward power in a mobile communication system which controls a base station transmitted forward power without influencing users conversations over the phone by gradually increasing the power.
2. Description of Related Art
A mobile communication system is generally employed for mobile units such as human beings, automobiles, ships, trains, and aircraft and includes a personal communication system (PCS), a digital cellular system (DCS), and a digital trunked radio system (DTRS).
FIG. 1 is a block diagram of a base station in the general mobile communication system.
As shown in FIG. 1, the base station comprises: a digital modulating part 1 for receiving coded voice information or data information and performing channel coding, digital modulation, and band expansion; a digital/analog converting part 2 for converting digital signals produced from the digital modulating part 1 into analog signals of intermediate frequency (IF); a base station management part 3 for managing parameters used in the base station and performing state management and source loading; a base station control part 4 for transmitting the parameters from the base station management part to another block and performing state management and call processes of the base station; a radio frequency control part 5 for controlling up-conversion of the IF received from the base station control part 4; a frequency up-converting part 6 for converting the IF outputted from the digital/analog converting part 2 into ultra high frequency (UHF) according to the control of the radio frequency control part 5; a power amplifying part 7 for amplifying a power of the UHF outputted from the frequency up-converting part 6; and a transmitting part 8 for performing bandpass filtering with respect to the signal amplified at the power amplifying part 7 to transmit only the signals of a desired band.
In the conventional mobile communication system, once the base station having such configuration receives the coded voice information or the data information, it performs the channel coding, digital modulation, and band expansion with respect to the information and, in turn, converts the information into analog signals of an IF band. Subsequently, the base station up-converts the IF signals into high radio frequency signals, amplifies a power of the signals, and transmits only signals of a desired band through the transmitting part 8.
In the mobile communication system, to activate a base station (cell or sector) is to make the base station transmit a predetermined power level fixed in accordance with a coverage area designed for the relevant base station to allow a mobile station within the coverage area of the base station to be given services. This activation is required when a new base station is established or a base station has been inactivated for a test or due to accidents such as natural disasters (e.g., the strike of lightning).
According to conventional technology, a base station (cell or sector) is activated in such a manner that it is made to instantly transmit a power having a predetermined strength fixed according to a coverage area of the base station. This instant transmission power causes a sudden increase of an overall forward link power, so a strong interference affects the forward link to a mobile station which is at a boundary between the relevant base station and an adjacent base station (cell or sector).
In other words, once a base station to be activated is started through a power on, the base station management part 3 in a base station adjacent to the base station to be activated controls the base station control part 4 to detect a base station activation command in accordance with the power on of the base station to be activated and the detected base station activation command is transmitted to the radio frequency control part 5. Subsequently, the radio frequency control part 5 controls such that the frequency of signals received from the digital/analog converting part 2 can be instantly up-converted according to the base station activation command transmitted from the base station control part 4. The power amplifying part 7, in turn, emanates the instantly amplified power to the coverage area, so that the power can be transmitted to mobile stations within the coverage area of the relevant base station which is adjacent to the activated base station.
At this time, the mobile stations are given the mobile communication services through forward traffic channels and the base station which has the mobile stations in its service area. The forward traffic channels for the mobile stations are interfered by the power which has been suddenly outputted from the adjacent activated base station. The base station adjacent the activated station then receives the interfered forward traffic channels of the mobile stations. Therefore, the sudden output of the power by the activation of a base station interferes the forward traffic channels of an adjacent base station covering the mobile stations, and the adjacent base station covering the mobile stations outputs an amplified power to its coverage area via the interfered forward traffic channels, thus deteriorating receive sensitivity of the mobile stations receiving the interfered power.
According to the conventional technology, in such case where the deterioration of the receive sensitivity is caused, a mobile station is allowed to receive the forward traffic channel where the interference is removed to a certain limit by increasing the power of a forward traffic channel of base station covering the mobile station, thereby improving speech quality.
However, there is a limit in such conventional method of controlling the forward power to solve the deterioration of performance of a link caused by the sudden and strong interference. The forward power control for the mobile station by the base station should be performed with an appropriate strength and at a right time. Otherwise, a pertinent call can be interrupted. For example, when a mobile station within the coverage area of a base station adjacent to a base station to be activated has a strong radio interference due to sudden output of a power of the base station to be activated, this significantly interferes with a normal forward traffic channel between the mobile station and its corresponding base station adjacent to the base station to be activated. In this case, the base station covering the mobile station and adjacent to the base station to be activated cannot receive the forward traffic channel of the mobile station, thereby disturbing the forward power control by the base station covering the mobile station, so the traffic channel between the mobile station and the base station covering the mobile station is interrupted.
The conventional technology which activates a base station (cell or sector) by making the base station to be activated instantly transmit a power of a predetermined strength has drawbacks of deteriorating speech quality of a mobile station and interrupting a call of the mobile station which is near a boundary in a service area of an adjacent base station (cell or sector).
To inactivate a base station is to cut off a transmission power of the base station, thus not allowing a mobile station in a coverage area of the base station to be given services. This inactivation is caused by a test for the base station or natural disasters such as the strike of lightning.
According to the conventional technology, the inactivation of a base station is effected by instantly interrupting a power transmitted from the base station. This instant interruption of the transmission power causes sudden reduction of a forward link power, so a strong interference affects a forward link of a mobile station near a boundary within a coverage area of an adjacent base station (cell or sector).
In other words, if the transmission power of a base station to be inactivated is instantly interrupted, a base station adjacent to the base station to be inactivated operates such that it can maintain forward traffic channels of mobile stations within its coverage area. The base station adjacent to the base station to be inactivated performs forward power control to instantly decrease the transmission power. As a result, a power strength of a forward traffic channel of a mobile station within the coverage area of the base station where the instant reduction of the transmission power occurs becomes to be changed.
When a transmission power strength of the base station adjacent to the base station to be inactivated exceeds a predetermined threshold, the mobile station within the coverage area of the adjacent base station cannot receive the transmission power from the relevant base station. Thus the relevant base station covering the mobile station which do not receive the transmission power cannot perform the forward power control, causing interruption of a call.
The conventional method of instantly cutting off a transmission power to inactivate a base station has a problem that a call made in a cell can be interrupted because the cell is suddenly inactivated.